It also is from the other vendors, other wise you could not play offline games aside from all games being very slow probs. They have DRM, you cannot play most games without a launcher (there are some games, most of my steam library is mostly DRM free but maybe cuz they were indie games) unless you crack it.

And requires authentication via Steam to launch. No steam, no game.

At least not unless third parties come up with a workaround.